Failure detection device for vehicle speaker

A failure detection device for a vehicle speaker includes a signal generator, an amplifier, a coupling capacitor, a supply circuit, a detection circuit, and a determination section. The signal generator generates a sound signal corresponding to sound outputted from the speaker. The amplifier amplifies the sound signal. The capacitor supplies the amplified sound signal to the speaker. The supply circuit supplies a direct-current test current to the speaker so that the test current does not flow through the capacitor by applying a test voltage to the speaker. The test voltage is higher than a voltage of the sound signal. The detection circuit detects a terminal voltage of the speaker. The determination section determines whether at least one of an open-circuit and a short-circuit occurs in the speaker based on the terminal voltage during application of the sound signal to the speaker.